Gas sample introduction devices for introducing a sample gas into the carrier gas flow supplied to the analytical column are widely used in gas chromatography analysis on gas samples. For sample introduction by this sort of gas sample introduction device, there is the scheme whereby a predetermined quantity of sample gas is metered by a metering tube provided in the channel and introduced into the analytical column, and the scheme whereby the sample gas is concentrated by a concentrating device provided in the channel and introduced into the analytical column, and devices are widely used which switch between and execute both schemes.
FIG. 4 illustrates the channel configuration of a conventional gas sample introduction device equipped with a function of switching between and executing sample introduction employing a metering tube (referred to below as metering mode) and sample introduction employing a concentrating device (referred to below as concentrating mode), as mentioned above. Eight-way valve 110 allows switching, by manual force or mechanical force, between two states: the connection state shown by a solid line and the connection state shown by a dotted line in FIG. 4. SVa through SVe are solenoid valves and Ta through Tc are branch tubes. It will be noted that, for each solenoid valve, NO signifies a normally open port, NC signifies a normally closed port, and C signifies a common port. It will be noted that gas inlet 162 and mass flow controller 150 serve to supply gas for pressurization of sample container 200 or gas for dry purging of concentrating device 130 at a predetermined flow rate, the details of which will be omitted here.
First, the operation of the metering mode in the device of FIG. 4 will be described. When the eight-way valve 110 is placed into the connection state shown by the dotted line and the solenoid valves SVd and SVe are switched to the NO side (i.e. the C side and NO side are connected), sample gas taken up from sample container 200 by needle 140 passes via ports d and e through metering tube 120, and is then discharged via ports h and a and solenoid valve SVd and branch tube Ta through gas outlet 172. Carrier gas supplied into gas inlet 161 from an unillustrated gas bottle or the like is fed into the analytical column via solenoid valve SVe, ports f and g, branch tube Tc and gas outlet 171.
With sample gas having flowed into the metering tube 120 in this manner, the eight-way valve 110 is switched to the connection state shown by a solid line in FIG. 4. As a result, the carrier gas starts to pass via ports f and e through metering tube 120, a set quantity of sample gas determined by the inside volume of metering tube 120, which was held in metering tube 120, is pushed out by the carrier gas and is fed via ports h and g and branch tube Tc toward the analytical column. It will be noted that the sample gas fed to the analytical column is divided into components in the process of passing through the column, and is successively detected by a detector as it comes out of the column.
Next, the operation of the concentrating mode will be described. When the eight-way valve 110 is placed into the connection state shown by a solid line and solenoid valve SVe is switched to the NO side and solenoid valve SVc to the NC side, sample gas collected by needle 140 passes via ports d and c through collection tube 131 provided in concentrating device 130, and is then discharged via solenoid valve SVc and branch tube Ta from gas outlet 172. Here, the collection tube 131 is cooled by an unillustrated cooling means, and in the process of the sample gas passing through the collection tube 131, predetermined components in the sample gas (sample components) are adsorbed inside the collection tube 131. It will be noted that the carrier gas supplied from gas inlet 161 here flows via solenoid valve SVe, ports f and e, metering tube 120, ports h and g, branch tube Tc and gas outlet 171 into the analytical column.
After the sample components have been adsorbed inside the collection tube 131 in this manner, the eight-way valve 110 is switched to the connection state shown by the dotted line, solenoid valve SVc is switched to the NO side, and solenoid valve SVe is switched to the NC side. Thereupon, the carrier gas starts to pass via solenoid valve SVe, branch tube Tb and solenoid valve SVc and through the collection tube 131 in the opposite direction to the sample gas previously. In this state, when the collection tube 131 is rapidly heated by an unillustrated heating means, the sample components which have been adhered inside the collection tube 131 are released at once, and the sample components at high concentration are carried by the carrier gas and flow out from collection tube 131, pass through ports c and b and branch tube Tc and are introduced into the analytical column. In this way, with the concentrating mode, even if the sample components are contained in the original sample gas in trace amounts, they can be fed into the analytical column after concentrating to increase their concentration, thus providing the effect of increasing the detection sensitivity.
In a conventional gas sample introduction device equipped with a function of switching between metering mode and concentrating mode as above, the metering tube 120 and collection tube 131 are connected in parallel, and sample gas fed out from one of these flows into the analytical column. Furthermore, all of the gas taken up into the metering tube 120 is introduced into the analytical column.
Patent literature 1—Japanese Unexamined Patent Application Publication H7-103956
In gas chromatography, a technique called the pre-cut method is known, whereby specific components are separated and removed from the sample gas before introduction into the analytical column (for example, see Patent literature 1). With the pre-cut method, the sample gas is taken up into the metering tube, after which a pre-column is interposed between the metering tube and analytical column and the sample gas inside the metering tube is introduced into the pre-column. The target component (generally, the low boiling point component) eluted first from the pre-column is introduced into the analytical column, after which the pre-column is disconnected from the analytical column before the unnecessary components (generally, high boiling point components) remaining in the pre-column are introduced into the analytical column. As a result, the unnecessary high boiling point components can be prevented from being introduced into the analytical column, which allows one to shorten the analysis time and to do without increasing the temperature of the analytical column, thus having the advantage of allowing one to extend the lifetime of the analytical column.
However, in order to execute this sort of pre-cut method in a conventional gas sample introduction device equipped with a function of switching between metering mode and concentrating mode as described above, it is necessary to provide a pre-column and dedicated channel switching system for pre-cut operation as described above in addition to the metering tube and collection tube, so the configuration of the device become more complicated, leading to increased size and higher cost of the device.
The present invention was made in view of this point, its object being to provide a gas sample introduction device capable of switching between and executing a metering mode and concentrating mode, which allows one to perform sample introduction by the pre-cut method without providing the aforementioned pre-column and dedicated channel switching system for pre-cut operation.